Sign, add text, highlight, and connect PDF documents together with these excellent apps.

The iPad Pro is great for many reasons, but I particularly love it for making paper documents and forms almost obsolete: I can't think of the last time I had to print a form and send it through the mail (or worse — fax it). Instead, I rely on iOS's built-in tools and great third-party apps to take care of all my form, document, and signature-related needs.

After testing a bunch of PDF markup apps — and asking for your favorites on Twitter, here are my top apps worth considering.

Markup isn't an app, but it's still pretty great

Preview may not exist on the iPad just yet, but its excellent markup and annotation tools are coming systemwide in iOS 11 as an extension. The Markup extension can be triggered by pressing either the Share button or new Markup button in certain apps — it looks like a pen tip with a circle around it. (You can also tap an email attachment in Mail.) 
In the Markup interface, you can add pen, highlighter, or pencil notation; basic shapes like squares, circles, arrows, and quote bubbles; drop a magnifier on the image or document; and even add text or a signature.

It's basic, to be sure, but sometimes basic is all you need — and once iOS 11 is released this fall, you'll have Markup features across the system at your fingertips.

Read more about Markup

PDF Viewer is a smooth alternative to Markup

While putting together this roundup, I had a number of people point me in the direction of PDF Viewer, a newer annotation app released at the end of 2016. After a few minutes with the free app, it's clear why they did — between its clean, simplistic interface and powerful annotation tools, PDF Viewer is a perfect in-between for users who need a bit more than iOS's Markup tool provides, but don't need the power of apps like PDF Expert or LiquidText.

A PDF app's interface can frequently appear daunting to the average user, thanks in part to the sheer number of annotation options developers try to shove inside of them, but PDF Viewer smartly simplifies this process. Taking a page from Apple's own iWork suite, the app provides a series of nested views depending on which feature you're using. For instance, if you're looking at a document, you'll be shown the tools for sharing, zooming, and browsing through annotations; tap the annotation button, and the app brings you into Annotation mode, with its various tools — still simplified into easy-to-understand icons.

PDF Viewer can even rearrange, delete, or insert blank pages within a PDF, though it doesn't have some of the more advanced combination features (like merging multiple PDFs or adding existing PDF pages into a document).

Twitter, you did well to bring this app on my radar. It's an excellent one.

PDF Expert is an annotation juggernaut

When people ask for an all-purpose PDF markup and annotation app, I tend to send them to Readdle and PDF Expert. The $9.99 app offers basic PDF reading, annotation, and digital signatures, but where it shines is in its advanced tools.

You can create customizable "stamps" for oft-used annotations (a friend to copy editors everywhere), edit the structure of the PDF, zip multiple documents together, password-protect your files, and sync with iCloud. A $6.99 Pro upgrade takes those tools one step further, and allows you to physically crack open a PDF and edit it on the spot. Have a spelling error in your ready-to-print proof? Even if you can't jump back to InDesign on your iPad, you can fix it in the PDF.

You may never need the tools that PDF Expert provides, but I for one love that an app this complex and functional exists on iOS.

Researchers, writers, and copy editors will love LiquidText

I've rewritten this intro to LiquidText about five times now, largely because the multitouch annotation app has this slippery way of defying description. A traditional sign-and-form-fill annotation app this is not: LiquidText is built for projects, novels, research papers, and dusty libraries. Lawyer and Mac enthusiast David Sparks describes it as being "engineered around the idea of reviewing long PDF documents better." It looks at books filled with post-it notes and string-covered bulletin boards and laughs. There's a better way to organize your research, and the app is it.

At its core, LiquidText focuses on the pain point of annotating lengthy documents, giving users a number of tools to do it in a way wholly unlike any other PDF app on the market. You can use multitouch gestures to pinch together large sections of a document; for instance, you could look an introductory thesis statement next to its midpoint argument to see if it properly connects the dots. You can pull annotations out from the document they belong to — like clippings or post-its — and organize them together or even link them along the right side of the screen. And all of this is lightning fast and wholly enjoyable, thanks to LiquidText's speedy and simple UI.

The Apple Pencil makes all of this even better, giving users specific gestures to highlight and pull out annotations as you review documents. For those who need this kind of workflow, there's no better app than LiquidText out there — and possibly no better workflow.

  • Free; $20 in-app purchase to unlock Pro features - Download now

Other apps we tested

For this roundup, I narrowed down an incredibly large pool of PDF apps to highlight the best ones in their respective classes, which naturally meant excluding otherwise beloved apps. Here are some alternative PDF annotation apps that are great, but didn't quite make the cut.

  • GoodReader, $4.99: GoodReader was my stalwart PDF manager and annotation editor for a long time, in large part because it supported uncompressing ZIP files, but I tend to look at it as more file management system than proper PDF annotation app.
  • GoodNotes, $9.99 & Notability, $9.99: Both of these apps have PDF annotation features, but they're first and foremost note-taking apps.
  • PDFPen, $19.99: Smile Software makes excellent apps, but as good as PDFPen on iOS is, it doesn't outshine PDF Expert.
  • iAnnotate, $9.99: iAnnotate was another app recommended by a number of Twitter users, but I don't find the interface or ease of use as enjoyable as working with PDF Expert.

Your favorites?


Do you have a favorite PDF annotation app I missed? Let me know below so I can check it out for our next roundup!